Predicting Perceived Quality of Life Scores From the National Eye Institute 25-Item Visual Function Questionnaire

Abstract

This study set out to determine the degree to which the composite score of the National Eye Institute 25-item Visual Function Questionnaire (VFQ-25) predicted perceived quality of life (PQoL) as measured by a single-item global measure of quality of life (QoL) and therefore, the extent to which the two were measuring the same construct. Hierarchical multiple regression was used to determine the ability of VFQ-25 to predict PQoL, while controlling for other variables significantly correlated with PQoL. The latter were entered as independent variables in the first step of this analysis and VFQ-25 in the second. This model determines the degree to which VFQ-25 predicted PQoL when all other variables were controlled for. Of the other variables assessed, only general health and group affiliation were found to be significantly correlated with PQoL. These variables, entered in step 1 of the analysis, explained 24.3% of the variance (adjusted r = 0.243) in PQoL. When VFQ-25 was entered in step 2, the model then explained 29.3% (adjusted r = 29.3) of the variance or an additional 5% when the effects of the other two variables were controlled for (r change = 0.050, p = 0.001). In other words, VFQ-25 only predicted 5% of the variance found in PQoL. Therefore, 95% of the variance was not explained by this measure. It is clear from the results of this study that VFQ and PQoL were not measuring the same construct. It is also apparent that the single-item global measure of QoL did indeed ask participants to rate their PQoL. Thus, we may conclude that the measure of vision-related QoL used in this study did not measure PQoL. Further research is required to determine the extent to which this finding may apply to other measures of vision-related QoL.